FIELD OF THE INVENTION
This invention relates to joints which interconnect sections of drive shafts to permit angular displacement between the sections, and more particularly, to a universal joint of the constant velocity type.
Shaft sections subject to angular displacement of their axes with respect to one another are commonly interconnected by a universal joint to permit one shaft section to drive another. The universal joint permits the sections to pivot at the connection, and also permits the transmission of rotary motion from one section to the other. On an automobile, a universal joint transmits power from the engine through a drive shaft, even though the engine is relatively rigidly mounted to the vehicle frame at a higher level than the axle, and the axle is constantly moving up and down in relation to the frame.
An ordinary universal joint, consisting of two yokes at right angles to one another and pivotally interconnected with a journal, causes a driven shaft to rotate at a variable speed in respect to the driving shaft. There is a cyclic variation, in the form of an acceleration and a deceleration of the speed, twice during each revolution. The extent of the fluctuation depends on the amount of angularity between the shafts. The greater the angle, the greater the variation in the speed of the two shafts during each revolution.
These velocity fluctuations result because the journal connecting the two yokes does not allow free movement other than a pivoting action. The journal wobbles as the joint rotates. When the journal tilts toward the output shaft, it adds to the rotary speed of the output. When the journal tilts away from the output shaft it subtracts from the speed of the output. The input and output shaft speeds are equal only when the journal lies in a plane which bisects the angle between the shafts.